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Centre for Evidence-
Based Medicine

Completed Systematic Reviews Worksheet for Evidence-Based Purchasing

Citation

Schierhout G, Roberts I, Alderson P. Colloids compared to crystalloids in fluid resuscitation of critically ill patients (Cochrane Review). In: The Cochrane Library, 4, 1998. Oxford: Update Software.

Are the results of this systematic review of therapy valid?

  1. Is it a systematic review of randomised trials of the treatment you are interested in?
    Yes. It compared the overall effects of colloid versus crystalloid fluids in a range of typical resuscitation situations. (NB it may be helpful to point out that "crystalloid" fluid is usually salt water [also known as normal saline]!)
  2. Does it include a methods section that describes finding and including all the relevant trials?
    Yes, they captured 48 apparently randomised trials from a wide search of the Cochrane Controlled Trials Register, MEDLINE, EMBASE and BIDS ISTP; by handsearching 29 journals and proceedings of international meetings; by checking reference lists and by contacting authors for information on any other published or unpublished trials. 37 of the 48 identified met the inclusion criteria. 19 of these were used to assess the outcome of death.
  3. Does it include a methods section that describes assessing their individual validity?
    Yes; inclusion criteria were randomised or quasi-randomised controlled trials; method of randomisation was checked with author and quality of concealment rated.
  4. Were the results consistent from study to study?
    Looking at the odds ratio table (see Summary of Analyses metaview in the Cochrane Library version, or page 964 in the BMJ), the results look fairly similar, in that there are not statistically significant differences between or within patient groups.

Are the valid results of this systematic review important?

Translating odds ratios to NNTs. The numbers in the body of the table are the NNTs for the corresponding odds ratios (or relative risks) at that patient's expected event rate (PEER).
Odds Ratios (OR)
0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5
Patient's Expected Event Rate (PEER) 0.05 2091 139 104 83 69 59 52 46 412
0.10 110 73 54 43 36 31 27 24 21
0.20 61 40 30 24 20 17 14 13 11
0.30 46 30 22 18 14 12 10 9 8
0.40 40 26 19 15 12 10 9 8 7
0.503 38 25 18 14 11 9 8 7 6
0.70 44 28 20 16 13 10 9 7 6
0.90 1014 64 46 34 27 22 18 15 125
  1. The relative risk reduction (RRR) here is 10%
  2. The RRR here is 49%
  3. For any OR, NNT is lowest when PEER = .50
  4. The RRR here is 1%
  5. The RRR here is 9%
Relative Ratios (RR)
0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5
Control Event Rate (CER) .05 200 133 100 80 67 57 50 44 40
.10 100 67 50 40 33 29 25 22 20
.20 50 33 25 20 17 14 13 11 10
.30 33 22 17 13 11 10 8 7 7
.40 25 17 13 10 8 7 6 6 5
0.5 20 13 10 8 7 6 5 4 4
.70 14 10 7 6 5 4 4 3 3
.90 11 7 6 4 4 3 3 2 2

Can you apply this valid, important evidence from a systematic review in caring for your patient?

  1. Do these results apply to your patients?
    Yes - the results suggest that crystalloids are probably at least as good as colloids for general use.
  2. Is your patient so different from those in the systematic review that its results can't help you?
    You could argue from these results that surgical patients might do worse on crystalloids (although the results were not significant, with the total number of patients small [191 in 7 trials] and number of deaths even smaller [9])

How great would the potential benefit of therapy actually be for your individual patient?

  1. Method I: In the tables on page 1, find the intersection of the closest odds ratio or relative risk from the overview and the CER that is closest to your patient's expected event rate if they received the control treatment (PEER):
    It is hard to calculate the weighted NNH from the numbers presented. Still, if you take the summary statistics of increased risk of death from colloids of 4%, then the NNH is 1/0.04 = 25. That is, if 25 people use colloids instead of crystalloids, one extra person dies. Alternatively, to turn this into an NNT, you could say that to avoid one death, you need 25 people to take crystalloids instead of colloids.
  2. Method II: To calculate the NNT for any RR and CER:
    NNT = 1/(CER(RR-1))
    Note that it is possible to do these calculations on any of the EER/CER presented in the Summary of Analyses (the RR table in the BMJ version)
  3. Method II: To calculate the NNT for any OR and PEER:
    NNT = (1-(PEERx(1-OR))/((1-PEER)xPEERx(1-OR))

Are your patient's values and preferences satisfied by the regimen and its consequences?

  1. Do your patient and you have a clear assessment of their values and preferences?
    Would need to check with patients/clients/population, but it is unlikely in this case that people - and their families - would be opposed to surviving resuscitation efforts!
  2. Are they met by this regimen and its consequences?
    Probably

Should you believe apparent qualitative differences in the efficacy of therapy in some subgroups of patients?

Only if you can say "yes" to all of the following:

  1. Do they really make biologic and clinical sense?
    Not really (surgery patients)
  2. Is the qualitative difference both clinically (beneficial for some but useless or harmful for others) and statistically significant?
    No
  3. Was this difference hypothesised before the study began (rather than the product of dredging the data), and has it been confirmed in other, independent studies?
    No
  4. Was this one of just a few subgroup analyses carried out in this study?
    Yes

Additional Notes

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